FS#9626 - Reverse simulator background logic

This patch reverses the logic of the simulator background image, showing it by default and having a –nobackground switch. The rationale is that new users almost invariably have difficulty figuring out how to control the simulator when all they see is the display, whereas experienced users will know to turn it off if it really bothers them.

I’m putting this patch here mostly to get some discussion about whether to do this or not.